1. Field of the Invention
One embodiment of the disclosed invention herein relates to power feeding devices, power receiving devices, and wireless power feed systems.
2. Description of the Related Art
Various electronic devices have spread, and a variety of products are in the marketplace. In recent years, mobile electronic devices such as mobile phones and digital video cameras are used very commonly. Further, electric propulsion vehicles, such as electric vehicles, which are supplied with power based on electricity, are showing up in the market.
In such mobile phones, digital video cameras or electric propulsion vehicles, batteries serving as power storage units (referred to as storage batteries) are incorporated. Currently, such a battery is usually charged with use of a household AC power source that is one of power feeding units, and by being directly contacted with the AC power. In a structure which has no battery or which does not use electricity charged in a battery, a device is operated by power directly fed from a household AC power source via a wire or the like.
On the other hand, researches and developments have been made on a system in which charging on a battery or power feeding on a load is conducted wirelessly, typical examples are an electromagnetic coupling method (also referred to as an electromagnetic induction method, see Reference 1), a radio wave method (also referred to as a microwave method), a resonance method (also referred to as a resonant method, see References 2 to 4).
As described in References 2 to 4, in a wireless power feed technique using a resonance method, a device that receives power (hereinafter, referred to as a power receiving device) and a device that feeds power (hereinafter, referred to as a power feeding device) each have a resonant coil. Further, in each of the power receiving device and the power feeding device, an electromagnetic coupling coil is provided. Feeding power from a power source in the power feeding device to the resonant coil and feeding power from the resonant coil in the power receiving device to a load are conducted by the electromagnetic coupling coils.
The resonant coil of the power feeding device and the resonant coil of the power receiving device are adjusted to resonate (LC resonance) at the same frequency.
When the resonant coil of the power feeding device and the resonant coil of the power receiving device face each other, they makes a resonant phenomenon, and thereby efficient power transfer is realized even when the distance between the resonant coils are large (see Reference 5).